Fluid processes conventionally exhibit severe limits on operation due to bed pressure drop, kinetics, and flow uniformity. These limits are placed on, for example, productivity, process efficiency, energy use, system size, environmental compatibility, and capital/operating costs. As one example of how these limits occur, the flow rate through a bed may be constrained because as flow rate increases, bed pressure drop increases. The pressure drop may reach a point where the pressure rating of a column containing the bed may be exceeded, the bed may begin to unacceptably compress, bed particles may be destroyed, and excessive energy may be required for operation. Clearly, this effect places limits on productivity (limits on flow rate) and design and cost (higher pressure requires additional structural strength). As another example, high linear velocities can result in unacceptably poor interaction or reaction of a fluid with the bed material. That is, the kinetic requirements of the system are self-limiting. An excessively high linear velocity of a fluid through a bed will result in an insufficient contact time of the fluid with the bed particles. Clearly, this places limits on productivity (again, flow rate is limited).
Spreading out a bed to a wide (large cross section) or shallow (shallow depth or short travel path) geometry instead of a high (long travel path), narrow (relatively small cross section transverse to the direction of flow) geometry will reduce both the bed pressure drop and the linear velocity of a fluid passing through the bed. While both of these effects would be very beneficial, such column construction is not prevalent because of the difficulty of distributing and collecting fluid across a wide, shallow bed (a large cross section). Any inhomogeneity or turbulence in the fluid introduced into the column cannot normally be attenuated through a wide, shallow bed so the inhomogeneities are reflected as inefficiencies and unacceptable processing. For example, in chromatography, such problems result in band broadening and poor separation of the components of a feed mixture.
A fluid treatment apparatus is disclosed in U.S. Pat. No. 4,673,507 to Brown, the contents of which are incorporated herein by this reference. The fluid treatment apparatus can be used for shallow bed operation. However this fluid treatment apparatus lacks significantly distributed fluid feed and collection systems and is dependent upon maintaining the bed in an overpacked condition where the particles are confined within the resin bed so that they are subjected to compression at all times. A substantially uniform fluid flow distribution across the bed is achieved by employing resins of fine (substantially uniform) particle size, which are maintained in the overpacked condition. This fluid treatment apparatus restricts process fluid flow across the bed.
U.S. Pat. No. 5,626,750 to Chinn, the contents of which are incorporated herein by this reference, discloses an apparatus for treating a fluid. In this apparatus, first and second “particle free cavities” are provided above and below a retained particle bed. Even flow of fluid through the retained particle bed is provided simply by the pressure drop across the retained particle bed, which is a function of the pressures in the first and second cavities. No provision is made to substantially control fluid flow characteristics (eddies, or turbulent zones) in process fluid streams near the surface of the retained particle bed.
U.S. Pat. No. 7,390,408 to Kearney, the contents of which are incorporated herein by this reference, solves the above problems using a shallow bed with distributors and collectors designed using fractal geometry. This type of vessel has become successful in industrial implementation and there are several benefits to this vessel design. For example, distribution and collection of fluids is extremely uniform. Because of the uniformity, very shallow beds of processing medium can be used without problems with channeling or non-coverage of the processing media. Pressure drop is subsequently very low, which means that the vessels using this technology can be rated for lower pressures than conventional devices. Heads of the shallow bed vessels are substantially flat plates in contrast to the spherical or dished heads of most conventional pressure vessels. In order to increase the capacity of the shallow bed vessels, their diameter must be increased, which leads to increased pressures on the heads. As the diameter increases, the pressure on the heads increases proportionally and mechanical support of the heads must be increased. The increased diameter increases the size and weight as the shallow bed vessels are constructed for higher capacity and higher throughput uses. The larger size also increases the amount of space occupied by the shallow bed vessels, making the shallow bed vessels more difficult to handle.
Filter presses have been used for more than 100 years to remove solids from a slurry or suspension. The filter press includes multiple filtration plates, each having a cloth filter and a chamber through which the slurry is passed. The slurry enters each of the filtration plates through a single port and the solids accumulate on the cloth filter as the liquid of the slurry passes through the filtration plates. The filtration plates have small holes for collecting the filtered liquid as the filtered liquid exits the filter press. Various methods of compressing and removing the solids (i.e., the filter cake) from the cloth filter have been developed. Following moisture removal, the filter cake is removed from the filter press by separating the filtration plates from one another and allowing the solids to drop out of the filter press by gravity. Uniform flow of the slurry through the filtration plates is not required because the solids are removed by filtration through the cloth filter.